The proposed research will complete the studies undertaken on HL- 14644, utilizing the experimental counterpulsation preparation developed for the isolation of suction (sink) or augmentation, and applying derived criteria to maximize the performance of circulatory assist systems. Experiments performed to date indicate that early or late timing and wave characterization of sink produce significantly differing effects on cardiac output and myocardial oxygen consumption. Preliminary data indicate that timing and tailoring of the diastolic augmentation wave may significantly affect the coronary flow and collateral circulation in shock states. Experimental series in a new closed chest model are proposed for the integration of optimal sink and/or augmentation, and to improve the effectiveness of intra-aortic balloon pumping, ascending aorta synchronized pulsation (AASP), left ventricle- AASP, and the femoral vein-AASP. Present and newly proposed modes of weaning from counterpulsation will be examined in the hope of elucidating the causes of clinically and experimentally experienced drastic rebound deterioration following sudden termination of pumping. In cases where enough viable myocardium is left and circulatory assist has achieved major improvement or normalization of cardiac function, sudden pump discontinuation may be very harmful. Study of more gradual transitions, without or with supplementary drug treatment, is proposed. The effects of counterpulsation on coronary collateral circulation will be examined, exploiting the easy communication, in the new closed chest model, with the region distal to the occlusion. Coronary autoregulation will be assessed at differing levels of simulated shock and during isolated sink and augmentation. The experimental studies will be performed in a new intracoronary balloon occlusion/reperfusion model, modified on HL-14644, which simulates shock through multiple sequential intracoronary occlusions, and which is well suited for assessment of hemodynamics, mechanical and metabolic regional as well as global cardiac function. Circulatory assist criteria will be assembled into a final report.